1. Field of the Invention
The present invention relates to an improved method for oxidizing and subsequently decomposing dihydroperoxides, and more particularly, to a method for oxidizing with hydrogen peroxide.
2. Description of the Prior Art
By well-known processes, diisopropylbenzene (DIPB) is oxidized to produce, among other products, the dihydroperoxides (DHP) and hydroxyhydroperoxides (HHP) of diisopropylbenzene, for the preparation of resorcinol. Almost all acid-catalyzed decompositions of m-DHP to resorcinol require the use of pure m-DHP. For example, U.S. Pat. No. 3,928,469 disclosed that a crude hydroperoxide mixture which is obtained from the oxidation product of m-diisopropylbenzene, and which has a composition consisting of 72% m-DHP, 20% m-HHP, and 8% others, is cleaved in a usual manner, using a mineral acid catalyst, to give only a low cleavage yield of about 70 to 73% resorcinol based on moles m-DHP used. Yet, there is no practical way to make pure DHP by the hydroperoxidation of m-DIPB and there is no economical way to separate HHP and other products from the hydroperoxidation product to obtain pure DHP.
The conversion of a hydroxy compound to a hydroperoxy compound by treatment with hydrogen peroxide is well-known. Therefore, it would be expected that conversion of m-HHP to m-DHP by hydrogen peroxide oxidation should not be difficult. However, conversion of most of the HHP in a DHP/HHP sample to obtain at least 90% pure DHP is not easy, especially if the reaction has to be completed during a short contact time as suggested in a review by Stanford Research Institute (SRI).
In 1972, researchers at SRI reviewed a new route for the preparation of resorcinol via hydroperoxidation. The SRI process involves production of m-DIPB by alkylation of benzene and/or cumene with propylene, followed by oxidation of the m-DIPB to DHP. The DHP is decomposed with the aid of an acid catalyst to form resorcinol and acetone.
The SRI review also proposed to use hydrogen peroxide to convert the small amount of HHP in the decomposition feed to DHP to improve the resorcinol yield on the assumption that the caustic extract contains no more than 10% HHP. Analysis of the caustic extract by improved techniques has revaled that the HHP content is much greater.
European Pat. No. 0021848, issued in 1983 to Mitsui Petrochemical Industries Ltd. discloses a process and apparatus for preparing phenols from alpha-hydroxyalkyl-substituted aromatic compounds. In the example, a methyl isobutyl ketone (MIBK) solution of an oxidation product of p-DIPB, which contains 24% p-DHP and 9.5% p-HHP (molar ratio of DHP:HHP=7:3) was reacted in a continuous manner with 60% hydrogen peroxide (H.sub.2 O.sub.2 :OH group molar ratio=0.92) and 3% sulfuric acid in acetone at 74.degree. C. and 1 atm and a residence time of 30 min. The hydroquinone yield was claimed to be 141% based on p-DHP, and 99.0% based on p-DHP+p-HHP. However, the patent disclosed no example of converting m-HHP to m-DHP with hydrogen peroxide.
Nakagawa et al. U.S. Pat. No. 4,283,570 issued in 1981 also to Mitsui Petrochemical Industries, discloses a two-step process to prepare resorcinol from a m-DHP/m-HHP mixture. In the first step, the m-DHP/m-HHP mixture obtained from the hydroperoxidation of m-DIPB is treated with hydrogen peroxide in the presence of an acid catalyst in a heterogeneous system of an aqueous aromatic hydrocarbon solvent under conditions which do not substantially cause the decomposition of DHP. The hydrogen peroxide oxidation is made in a continuous manner while removing by-product water as an azeotrope with the aromatic hydrocarbon. The second step is the acid-catalyzed decomposition of the product of step 1 in the substantial absence of hydrogen peroxide. The patent further discloses that the second step can be performed by contacting with a solid catalyst, such as a cation exchange resin or silica-alumina, or with an inorganic or organic acid. A more detailed description of step 1 alone is reported in yet another Mitsui Petrochemical Industries patent, Imai et al. U.S. Pat. No. 4,267,387. In this patent, the reactor temperature is maintained by feeding a vapor of aromatic hydrocarbon solvent. The patent also stressed the importance of removing co-product water as an azeotrope with the aromatic hydrocarbon solvent.
It has been observed that the hydrogen peroxidepretreated reaction product still contains significant amounts of moisture and when such product is decomposed with either a solid catalyst or an inorganic acid catalyst such as sulfuric acid, a large quantity of m-isopropenylphenol is formed as by-product. The selectivity to resorcinol remains at about 70%, which is the same as the selectivity observed using reaction product which has not been pretreated with hydrogen peroxide.
The decomposition of m-DHP to resorcinol is usually carried out in the liquid phase, in a substantially anhydrous organic solvent, such as acetone, MIBK, benzene, or toluene. The decomposition is highly exothermic, and produces one mole of resorcinol and two moles of acetone from each mole of m-DHP. Small quantities of strong acids, for example, sulfuric acid or orthophosphoric acid (H.sub.2 SO.sub.4 and H.sub.3 PO.sub.4, respectively), are used as catalyst. ##STR1##
The rate of DHP decomposition is thought to be first order based on DHP; it is accelerated by acid and by resorcinol but retarded by water. All hydroperoxides present in the feed will be converted to acetone and corresponding phenolic products. Thus, m-monohydroperoxides (m-MHP) will form m-isopropylphenol and m-HHP will form m-(apha-hydroxyisopropyl)phenol, which immediately dehydrates to m-isopropenylphenol.
According to the SRI review referenced above, the MIBK extract of m-DHP is evaporated to produce a 50% solution of hydroperoxides. Concentrated sulfuric acid (0.2 wt %), as catalyst, and 70% hydrogen peroxide (25% excess) to oxidize HHP and the dicarbinols (DCL), are added to this solution in a continuous reactor at 80.degree. C. The addition rates are such that an eight minute residence time is achieved. After the cleavage, the sulfuric acid is neutralized with a slurry of hydrated lime and the solids are removed by filtration. The filtered cleavage product is distilled to remove acetone and MIBK. The aqueous distillation bottom is extracted with toluene to selectively remove impurities (isopropylphenol and heavy ends) from the aqueous resorcinol solution. The purified aqueous raffinate is evaporated to remove part of the water. The concentrated aqueous solution is allowed to grow crystals. Finally, the resorcinol is separated by centrifugation and dried.
However, according to British patent specification No. 1,455,450, published on 1976, only by using pure m-DHP for the acid-catalyzed decomposition can relatively pure resorcinol be obtained. When product from the hydroperoxidation of m-DIPB is directly used in the decomposition, the resulting reaction product contains, besides resorcinol and the compound produced from other hydroperoxides, a number of other secondary products formed by subsequent reactions of the decomposition components and products under the action of acid catalyst. Resorcinol and acetone react to form resins and resorcinol and isopropenylphenol react to give a high-boiling adduct. The isopropenylphenol also polymerizes to give both liquid and solid polymers. The chemistry involved when a DHP/HHP mixture is decomposed in the presence of acid-catalysis presented below. ##STR2##
Similarly, Suda et al. U.S. Pat. No. 3,923,908 to Sumitomo Chemical Company discussed the relationship between DHP purity and the resorcinol yield from its decomposition. The yields of resorcinol are highly dependent on the amount of impurities containing the 2-hydroxy-2-propyl group, such as carbinols and HHP. Best results (90-95% yields) are obtained when the ratio of these groups to the number of molecules of DHP is below 0.16. In other words, the mol % HHP in the DHP/HHP sample can not be greater than 14%. A way to obtain such a high purity DHP/HHP sample is not mentioned in the patent.
Imai et al. U.S. Pat. No. 4,339,615, issued in 1982 to Mitsui Petrochemical Industries, disclosed a process for producing resorcinol, which comprises cleaving pure m-DHP in the presence of a water-soluble acid catalyst (sulfuric acid in acetone) in a mixed solvent consisting of an aromatic hydrocarbon and acetone. An 86% resorcinol yield is reported using a DHP/HHP sample containing 3.9 mol % HHP. The pure DHP probably is obtained by treating their hydroperoxidation product with hydrogen peroxide.
British Patent Application GB No. 2 071 662 A discloses the use of superacid catalysts, such as boron trifluoride-hydrogen fluoride complex for the preparation of resorcinol from m-DIPB.
Many patents have disclosed procedures for the purification of crude resorcinol obtained by decomposing m-DHP with acid catalysts. For example, a Japanese patent, Japan Kokai 78-53626, issued to Sumitomo Chemical Company claims a simple distillation process to obtain pure resorcinol. Crude resorcinol from the DHP decomposition is distilled in vacuo at less than 210.degree. C. pot temperature to effectively remove impurities produced in the acid-catalyzed decomposition.
Another patent, Hashimoto et al. U.S. Pat. No. 4,239,921, issued in 1980 to Mitsui Petrochemical Industries, discloses an improved resorcinol purification by solvent recrystallization. The patent claims that both low-boiling and high-boiling impurities can be removed from the crude resorcinol by a recrystallization process using a mixed solvent consisting of a specific ratio of an aromatic hydocarbon, an alkylphenol, and an acylphenol. For example, the resorcinol recrystallized from a mixture of toluene-isopropylphenol has only 30 ppm of high boiling and 60 ppm of low boiling impurities.
An object of the present invention is to improve the purity of m-DHP. A further object of the present invention is to improve the yields of resorcinol via the subsequent decomposition of m-DHP.